TIMES photograph by Annette Beard Pea Ridge Water/Wastewater Department superintendent Ken Hayes looks over the lagoons at the Pea Ridge Sewer Treatment Plant Tuesday morning as he explains the source of the sulphur odors eminating from the plant recently.

Below freezing temperatures for the last week of December and first week of January dropped the temperature of the sewer lagoons to 32.8 degrees killing essential bacteria.

Ken Hayes, superintendent of the Water-Wastewater Department, said when the lagoons' temperatures drop below 37 degrees, the "bugs" start to die.

City officials have received complaints from people asking about the source of the stench. Depending on the weather, the malodorous smell is noticed most near the plant, north of downtown. When the winds were from the north, Hayes said it could be smelled as far south as the Water Department office on North Curtis Avenue. When it's rainy, the air is heavy and the odor "mushrooms out" and is noticed most close to the lagoons.

The sewer treatment plant is a lagoon system that depends on bacteria breaking down the sewage. When temperatures drop below freezing for a week or more, then the necessary bacteria is killed.

"It's not an indication of things not working right," Hayes said, adding that there is no health risk associated with the unpleasant smell. "It's a result of cold, cold temperatures."

Excessive rains this spring have pushed the four lagoons to the brink of touching, although rain also dilutes the sewer water.

"Warm temperatures will help," Hayes explained. "The up and down temperatures are not helping."

Showing a graph of the amount of oxygen in the lagoons, Hayes explained that the employees turn on more diffusers in the first lagoon to increase oxygen in the lagoon.

"The oxygen we're putting into the bottom of the lagoon is being consumed, it's not even making it to the top," he explained. "It's struggling to come back."

Hydrogen sulfide is created by the process causing the unpleasant odor about which people are complaining.

The current plant is designed for a capacity of 300,000 gallons and about 340,000 to 350,000 gallons are being pushed through. The city has approved a new plant which will help with the capacity.

"Even with new plant, you're basically farming bugs and the bugs do all the work. It's organic matter, bugs feed off it and reproduce," Hayes said. "We're fighting getting bug activity back where it should be."

"We're doing what we need to do and what we're supposed to do; it's just going to take some time," Hayes said, adding that "typically when the air warms up, the conditions improve."

Hayes said that most lagoons are only four to five feet deep and the Pea Ridge lagoons are are 11 feet deep. They are designed to have three zones -- an anaerobic zone at the bottom where the bugs that don't require oxygen live. The top zone is the aerobic zone.

"It's a facultative lagoon -- means you have both aerobic and anaerobic zones," he said, explaining that the bottom zone is basically sludge and will break down much slower.

"It's Mother Nature," Hayes said.

Four years ago, there was a similar situation with extremely cold temperatures for a week, but there was less sewage going through the plant.

"At ADEQ, they know our situation," he said, referring to the governing agency -- the Arkansas Department of Environmental Quality."

Hayes said approvals have all been completed on the new sewer plant. "It's been a long two-year project but should go to bid in the next 30 days."